Divergent Enzymatic Assembly of a Comprehensive 64‐Membered IgG N‐Glycan Library for Functional Glycomics

N‐Glycosylation, a main post‐translational modification of Immunoglobulin G (IgG), plays a significant role in modulating the immune functions of IgG. However, the precise function elucidation of IgG N‐glycosylation remains impeded due to the obstacles in obtaining comprehensive and well‐defined N‐glycans. Here, an easy‐to‐implement divergent approach is described to synthesize a 64‐membered IgG N‐glycan library covering all possible biantennary and bisected N‐glycans by reprogramming biosynthetic assembly lines based on the inherent branch selectivity and substrate specificity of enzymes. The unique binding specificities of 64 N‐glycans with different proteins are deciphered by glycan microarray technology. This unprecedented collection of synthetic IgG N‐glycans can serve as standards for N‐glycan structure identification in complex biological samples and the microarray data enrich N‐glycan glycomics to facilitate biomedical applications.